The present invention is generally related to improved steering devices for vehicles, and more particularly to steering devices for vehicles having a steerable rear tag axle.
As the population of the world has escalated, the amount of waste produced has risen and the need for larger refuse trucks having a higher carrying capacity has intensified. However, with the increase in size and length of the trucks, it is becoming more difficult for the larger refuse trucks to maneuver through the city streets, cul-de-sacs and alleyways. Additionally, many state and federal laws limit the length between the axles and the maximum gross vehicle weight. To comply with these laws, an additional axle, otherwise known as a tag axle, is mounted rearward of the drive axle to accommodate the additional weight of the vehicle. The three conventional types of tag axles are fixed tag axles, self-steering tag axles and steerable tag axles. The conventional tag axles, however, suffer from a number of disadvantages.
Fixed axles typically do not turn and are often used as a second drive axle. Fixed axles do not reduce the turning radius, and can actually increase the steering radius of the vehicle because the fixed tag axle push the drive tires through the turn. Moreover, the fixed tag axle tires often scuff during the turning of the vehicle, which reduces the life of the tires and increases the cost of maintenance for the vehicle.
Conventional self-steering tag axles turn independently of the front steering axle and must overcome a certain amount of resistance to move from its straight orientation to a turning orientation. Because the self-steering tag axle systems must overcome the resistance, excessive tire wear and tire scuffing often occurs. Moreover, conventional self-steering tag axles must often be locked in a straight orientation or raised off of the ground entirely when the vehicle moves in reverse. Such configurations do not improve the steering radius of the vehicle, and can actually detrimentally affect the other axles when the vehicle moves in reverse.
Conventional steerable tag axle systems, such as those described in U.S. Pat. Nos. 5,364,116, 5,329,451 and 5,135,064, use a complex and expensive system of control valves and linkages to help turn the tag axle wheels. Although these steerable tag axle systems can provide a tighter turning radius than the fixed or self-steering tag axles, because these conventional steerable tag axles are so complex, additional maintenance is often required.